Telephone trunking system.



Patented Apr. 25, 1916.

' 4 $H EETSSHEET l- IIIHHI A a 'f Zwa/mzz E. n. FALES. TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED new, 1'908.

' E. 0. FAL'ES. TELEP'HONETRU-NKVIN'G SYSTEM.

APPLICATJQN man mac. 1.190s. I Patented Apr. 20, 1916.

' 4 5HEETSSHEET 2.

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E. D. FALES. TELEPHONE TRUNKING SYSTEM. APPLICATION FILED 020.1. 1908.

4 SHEETS-SHEET 3- Patented Apr. 25, 1916.

. UNITED STATES PATENT OFFICE.

EDWARD D. FALES, LA GRANGE, ILLINOIS; ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE TRUNKING- SYSTEM.

To all whom it may concern: Be it known that I, EDWARD D. FALEs, a citizen of the United States of America, and

- resident of La Grange, Cook county, Illinois,

have invented a certain new and useful Improvement in Telephone Trunking Systems, "of which the following is a specification.

My invention relates to trunking systems for telephone or other service, and it relates more particularly to two-way trunks for use in automatic telephone exchange systems, as, for example, trunking in opposite directions between two automatic exchanges, although in certain respects, as will hereinafter ap pear, my invention is not limited to either a two-way or-a one-way trunk.

In certain respects my invention has to do with the type of system shown in my Patent No. 1,064,719, issued June 17, 1913, for improvement in telephone trunking systems.

Objects of my present invention are to provide an improved two-way trunk-line having a non-numerical trunking switch at each end thereof, whereby the seizure of either end of the trunk-line serves to automatically operate a non-numerical trunking switch at the other end thereof, and to thus automatically extend connection therefrom to an idle switch, such, for example, as a selector or connector, according to' the size and character ofthe exchange; to provide an improved two-way trunk in a three-wireautomatic telephone exchange systemthat is to say, in a system in which the subscribers control or operate the automatic switches by means of a ground and two metallic condoctors; to provide an improved three-wire system in which non-numerical trunking switches are provided for extending connection from one set of numerical switches to another, such non-numerical trunking switches being previously interposed between the said numerical switches, as, for example, between first-selectors and second selectors, as herein shown; to provide an 7 arrangement in a three-wire system whereby whenever the numerical switch is disconnected from the trunk provided with the non-numerical trunking SWltCllGS, all of the switches of the said trunk are automatically restored'to normal condition, putting the trunk in a non-busv condition at both ends,

whether the disconnecting operation of the numerical S\\'ll'.(ll has been effected electri- Specification of Letters Patent.

Patented Apr. 25, 1916.

Application filed December 1, 1908. Serial No. 465,561.

cally or otherwise, as, for example, by hand; and to prov de certain details, combinations and features of improvement tending to increase the general efiiciency of a telephone exchange system of this particular character, as will hereinafter more fully appear.

In the accompanying drawings Figures 1,

2 and 3 are a diagrammatical representation of the essential features of the master switch E shown in Fig. l.

The exchange in which the calling subscriber shown in Fig. 1 is located will be designated as exchange A. This exchange is provided with a central battery B having a terminal preferably grounded at G. This battery may be used for supplying all talkmg and operating current to the exchange A.

Of the apparatus allotted to the exchange A the drawings show the calling subscribers station C, the line switch D allotted to the said statioin and individual to the same, but controlled, together with a number of similar line switches, by the common mechanism E usually known as the master switch. Accessible to the line switch D is the numerical switch F usually known as the first-selector, which is one of a group of selectors common to a number of line switches D. Through the medium of the selectors F the two-way trunks of my invention, such as the two-way trunk H, may be reached by the subscriber C, as indicated in the drawings. The. selectors F may or may not have access solely to two-way trunks H. The arrangement may be such, for example, that the selector F will have access to trunks H from only a certain level, or from certain levels, while from still other levels other switches, such as second-selec-v The said connection is esexchange A 2o teries, inasmuch as In like manner the trunk fif although' usual manner, h section of the two-way tru'nk H to the left trolled by a master switch. The exchange to which the called subscriber J belongs will be designated as the A -exchange, which exchange comprises the called subscribers line switch D, and which line switch is 1denminal at the :\-exchange ol the trunk-line,

which, at the A-exchange, terminates in the non-numerical switch l. In the A -exchange there is shown another battery B having a terminal preferably grounded at i. This batteryinaybe used for supplying all talking and operating current to the supplied withcurrent from separate batasingle battery may be used for the purpose." It will be understood that in the. usual arrangement the line switch D (Fig. 1) is provided with a bank comprising the terminals of ten 'trunks, each t'runk being aduplicate of the trunk shown which terminates in the selector-F, It'w'ill alsobe understood'tha't each of these trunks is made (JOIl'lll'lOnrtO allot the line switches of a group, as, for example, com

anon to all ofthe line switches controlled by the master switchjE, and it IS obvious, I

"exchange to the i k-exchange, as, for extherefore, that, although the trunk running from the selector F to the line switch D is shown with only one line switch bank. terminal, this trunk is in reality provided with as many terniinals as there are line switches.

shown with only one bank terminal inthe selector F, has in reality as many multiples as there-are selectors to which this trunk H is common. in a 'si-milarunanner the nonnumerical switch M at the A -exchange is I rovided with ten trunks, each terminating 1n a selector L, while the selector F has access to the two-way trunks H just as the selector switch F inFig. lha's access to the said trunks H, Of course, the second-se lector' L has access to connectorsK in the It will'be seen that that of'thedotted line found in Fig. 2 is an exact 'duplicateof the section to the right-thereoi'.

'In'general the mode of operation is' as follows: VVhenthe'subscriber 'C {Fig.f-l) wishes to call the subscriberJ (Fig. 3) the subscriber C removes his receiver, thereby operating the line switch D to establish con-' nection with the selector F; The selector F- isthen operated bythe subscriber C upon the firstmove vof his dial." This first move of the dial raises the wiper of the selector F to a certain bank level, from which the switch, by automatically rotating, automatifrom the A -exchange. stood that by this operation the trunk is It is not absolutely essential that these exchangesA and A should be- ,nector following is the same rious instance explained. It should be ally picks o-utthe first idL-j two-way trunk is operated to establish connection with the second-selector L. ()f course,the selector F makes the trunk H busy at,the A-exchange at all other selectors F to which the said trunk H. is accessible at the A-exchange. At the A -"xchange the operation of the line switch M makes the trunk busy to all switches which have access to the trunk H It will be underniade instantly busy at both ends. When the line switch M establishes connection with the selector L it cuts itself off from the -trunk ,-thus giving the calling subscriber C a clear line from the A-exchange to the A- exchange. Bythe second operation of the similar manner to the selector F to find the connector K. The said connector now, as is usually the case, responds to the last two. operations of the calling subscribers dial,.

-ihe calling subscriber hangs up his receiver,

11 of the switches are restored. .It will be be seen that when a call passes from the A ample, when the subscriberJ calls the subscriber C, the order of operation is exactly reversed. First theline switch D operates 'to-connect with the-selector F which in' turn responds to the first operation of the dial at the station J and finds the two-way trunk H. As soon as the connection is established with the said trunk the line switch M is cut off from the trunk, while the line switch isc'aused to operate to establish connection with a suitable switch similar to the selector L, Fig. 2, and from there on the.

operation of this selector and of the conas in the prestated here that whether the selector F at the A-exchange is operated to establish-com nection with the trunk H electrically as whenthe subscriber G is calling, or mechanically as when an exchange attendant manip- 'ula tes the selector F, the non-numerical switch I is cut ofl" and the non-numerical. switch M is operated just the same. After the switches I and L have been thus once operated they are automatically restored when the selettorjxF is disconnected from the trunk, whcther this operation is done electrically as y the calling subscriber C, or mechanically as by, the exchange attendant by manual wpei'ation. In other words, the restoration of the switches l and M is dial the calling subscriber operates the second-selectorL, which latter operates in a scribers instruments, the subscribers line exchange.

Having thus outlined the general mod of operation, a more detailed description will now be given as follows: The subswitches, the master switches for controlling these subscribers line switches, the firstselectors, the second-selectors and the connectors are of the type shown and described in the W estem E Zectfician of January 11, 18

and 25, 1908,.and also described in English Patent No'[ 26,301 of, 1906. -More specifically, however, the telephone; is provided with the usual transmitter 2, induction-coil 3,'receiver 4,.switch-hook 5 and ringer 6. In additiom it is provided with the usual calling mechanism comprising the impulse wheel '7 having on its periphery the-impulse teeth 8 for operating the impulse springs 9 and 10. The'said impulse wheel 7 is, of course, mounted on the same shaft 11 as the dial, being rigidiwith the same. Normally that is. when theswitclrhook is downthe bell 6, ishridged across the line conductors Band 13 through the condenser 14. For

' 30 'releasing purposes the telephone is also provided with the release springs 15, 16 and 17, the spring 15 being connected with the socalled ground'post 18 which is normally disconnected from the groundspring 19. The connection between the springs 18 and 19,

' however, is made whenever the dial is moved, thereby supplying ground notionly for releasing purposes but for calling purposes as well. I

The line switch D comprises a trip magnet 20, a release. magnet 21 and a bridge-cut-off relay 22. The trip magnet 20 is designed to operate the usual plunger for pressing the bank springs 23 and 24, 25 and 26, 27 and 28, and 29 and 30 into contact. This plunger may be arranged as shown in the Western Electrician publicationspreviously mentioned, so that when in normal position it is under the control of the master switch E,

whereby the said plunger may always be removed from opposite a busy trunk to a position opposite an idle trunk. The said master switch E is provided with a motor magnet relay 31, a motor magnet 32, an auxiliary relay 33 for opening the circuit of all trip magnets 20 of a group while the master switch is operatingover the .master switch bank a, and with an operating wheel 0 directly connected with the shaft through the medium of. which the plungers are controlled.

The selector switch F, which is of the type shown in United, States Letters Patent No. 815.321, issued March 13, 1906, to Keith.

"' Ericksqm & Erickson, is provided with the" Of course, the same is true.

usual vertical line relay 34, rotary line relay 35, vertical magnet 36, rotary magnet 37, release magnet 38, private magnet 39 and back-release relay 40. The selector F (Fig. 3) is provided with exactly the same magnets, namely the vertical line relay 41, rotary line relay 42, vertical magnet 43, rotary magnet 44, release magnet 45, private magnet 46 and back-release relay 47. The selector switch L is likewise provided with the Vertical line relay 48, rotary line relay 49, vertical magnet 50, rotary magnet 51, release magnet 52, private magnet 53 and back-release relay 54.

The connector switch K, which is of the same general character as the connector switch shown in United States Letters Patent No. 815,176, issued March 13, 1906, to Keith, Erickson & Erickson, is provided with a vertical line relay 55, rotary line rclay 56, vertical magnet 57, rotary magnet 58, release magnet 59, private magnet 60, ringer relay 61, front-bridge double-wound relay '62, and back-bridge double-wound relay 63. The line switch D? of the called line being the same as the line switch D and being likewise represented, the magnets 64, and 66 are, respectively, the trip and release magnets and the bridge-cut-oft relay. It will be understood, of course, that this line switch, together with other line switches of the same group, are controlled by a master switch the same as the master switch E.

At the A-exchange there is allotted to the two-way trunk H, in addition to the nonnumerical switch I, a set of auiriliary backrelease relays 67 and 68 for controlling the release of the switches that have established connection with the trunk. These relays will be referred to as the vertical auxiliary back-release relay 67 and the, rotary auxiliary back-release relay, 68,6 ,In addition, there is provided the relay 69 for controlling the release of the apparatus at the A- exchange, which will be referred'to'as the forward release relay. There are also provided two additional relays 70 and 71, the

former 70 for removing ground from the plunger-operating winding 72 of the nonnumerical trunk switch I and supplying operating current to the bridge-cut-ofi winding 7 3 of the said trunk switch when a call is being sent from the A-exchange 'tothe A exchange, and the latter 71 for breaking the energizing circuit of the relay 7 0 and for supplying guarding potential at the private bank contact 74 of the selector switch F at the A-exchange and all multiples of the said contact 74 when a call comes fgom the A exchange to the A-exchange. The resistance 75 shown in the,,rele;ise', ,circuit con trolled by the auxiliary bac r ielease relays 67 and 68 is to cor trol the flow of current through the lowrwdnd bacli-release relay 40fof the selector, The non-numerical A exchange,

78 and 79 .end the plunger armature 80.

These various armatures control the springs 81, 82, 83,84, 85, 86, 87 and 88 in the manner hereinafter fully described. The magnetic circuit of the. winding 77 is made separate from that of the windings 72 and 73 by the lateral projection on the core, by means of-which the magnet 76 is attached to the bracket 7 6. Although the arm 80 is included in the magnetic circuit of the winding 73, as well as that of the winding 72, the winding 73 is not strong enough to attract the arm 80 from its normal position, but has suflicient strength to maintain said arm in its operated position after it has been drawn down by the winding 72. The armature 79 may be operated by either the winding 72 or the winding 73. The two-way trun 'H is also provided at the A-exchange with an addditional auxiliary relay 89 for opening the rotary side of the trunk and sending an impulse over the rotary side of the trunk to the A -exchange when a call is going from the A-exchange to the A -exchange. Since the apparatus allotted to the trunk H at the A -e'xchange is an exact duplicate of that allottedto the said trunk at the it will be observed thatflthe relays 67 ,68, 69, 70, 71, 76 and 89 are duplicated by the corresponding relays 90, 91, 92, 93, 94, 95 and 96. Similarly the resistance 75 at the A-exchange is duplicated by the resistance 97 and the trunk-release circuit controlled detailed description.

controlled by the auxiliary back-release relays and 91, the windings: 72,73 and 77 of the non-numerical switch I are duplicated by the windings 98, 99 and 100 in the non-numerical switch M; likewise the springs 81 to 88, inclusive, in the switch I perform similar functions as the springs 101 to 108, inclusive, while the armatures' 78, 79 and 80 perform functions similar to the armatures 109, and 111 of the line switch It should be understood that the nonnumerical switches I at the .A-exchange are bya master switch just as the non-niunerical switches M at the A-exchange are controlled'by the master switch E. Thismaster switch is provided with a motor relay 112, motor magnet 113, the auxiliary relay 114 for, preventing any of the line switches M from DIRT flung while the master-switch E is operating, and in addition the relays 11p and'116, the uses of which will become apparent in the course of the It will be seen that the relay 115 is'connected to the magnet 95 "of the line switch M at a. point between the windings 99 and 100. In like manner the magnet 76 of the line switch I is connected to a relay similar to the relay 115 at apoint between the windings 73 and 77. It will magnet 20 to also be seen that the winding 980i the magnet 95 is connected to the top spring of the, .relay 115.

Having thus pointed out the details of the apparatus, the circuits and operations will now be more easily understood. Assuming that the number of the subscriber J is #2220, the subscriber C proceeds to operate his 'dial in accordance with the digit 2, after having removed his receiver. In thus rotating the dial he first causes the springs 18 and 19 to come into contact, thus supplying operating current for the. impulse springs 9 and 10. Upon advancing from normal positionthe dial carries the rotary spring 9-into engagement with the ground post 18, thereby energizing the trip magnet 20 of the line switch I) by a/flow of current from ground G at thetelephone C over the rotary conductor 13, and through the trip battery lead 117, thence through battery B ,to ground G. By attractin its armature the trip'magnct 20 unlocks tie plunger which is resting opposite an idle trunk, assumed in this case to be'the trunk running to the switch F, which plun-.

ger then presses the springs 23 and 24, the springs 25 and 26, the springs 27 and 2, and the springs 29 and 30 into contact as shown. It will be seen, of course, that the engagement of the springs 23 and 24: on one side, and the engagement of the springs 29 and 30 on the other, extends the calling subscriber-"s line to the switch F. It will also be seen that the closure of contact between the springs 27 and 28 supplies ground to the rent for energizing the private cut-ofi' relay 22 which thereupon energizes and connects the vertical line conductor 12 with the vertical normal conductor 119, atthe same time disconnecting the trip magnet 20 from the line. Theplunger being in the nature of a disconnector has no tendency to return to normal position after having once been operated. It is not necessary to maintain the trip magnet 20 energized It will be noted that the closure of coritact between the springs 25 and 26 establishes a non-grounded potential at the first contact of the master switch bank n by way of the conductor and through the release or restoring mag-,

net 21. This guarding potential serves to drive the master switch from opposite the trunk running to the switch F, and also prevents the master switch from ever stopping on this trunk again as long as this guarding potential is maintained at the said point, designated/as 121. The master driven on because theinotor relay 31 is enerswitch is gized, which relay, by pressing the springs 122 and 123 into contact, closes an energizing circuit through the motor magnet 32. This motor magnet energizes a number of times and thereby rotates all plungers in normal position opposite the next trunk. The energizing circuit for the magnet 32 is maintained by the springs 124 and 125 being brought into contact at the first impulse of the magnet 32, but these two springs 12st and 125 are separated as soon as the master switch reaches the next trunk, and, of course, since the naster switch bank wiper 126 has leftthe contact 121, the energizing circuit for the motortelay 31 is broken, thus bringing the master switch to a standstill.

. It will be seen, however, that if the next trunk is busy the contact 127 will also have a guarding potential just as the contact 121 as aguarding potential, and the master switch will be advanced to the next step and so on until an idle trunkis found.

It will be seen that in multiple with the motor magnet the slow-acting relay. 33

energizes and opens the connectionbetween all trip magnets 20 and the battery B of the group'of line switches D controlled by the master switch E. The object of this arrangement is to prevent any subspriber from tripping into a busy trunk while the master switch E is passing over such busy trunks.

Having thus extended connection to the switch F and caused the master switch to drive all other line switches D from opposite-the trunk of the said switch Fby the time that the subscriber is ready to let the dial run back, the impulses which are transmitted by the dial on its returnmotion are then taken up by the switch F for carrying that switch to a given level (in this case the second level). and then causing it to automatically pick out the first trunk H- that is idle. As the dial returns toward normal, the rotaryspring 9 having in the meantime disengaged from the spring 18, the vertical impulse spring 10 is pressed onto the spring 18 twice, thereby sending two impulses over the vertical line conductor 12, and through the vertical line relay 34 of the switch F to battery B and to ground G. After thesevertical impulses have been sent in the rotary spring 9 is again pressed onto the ground spring 18 once, thereby sending another impulse over the rotary conductor 13. which now operates the rotary line relay 35 once. The vertical line relay 34, upon energizing twice, in turn closes the energizing circuit of the vertical magnet 36 twice from ground G through the said vertical magnet to battery B. By

this operation the shaft and Wipers ot' the switch F are raised opposite the first contact of the second level, thereto remain until the rotary impulse comes in. The rotary line relay 3), in response to the rotary impulse, then closes an energizing circuit for the private magnet 39 from ground. Gr through the said private magnet to battery B. This private magnet, upon energizing and definergizing, trips the side switch to second position, thereby carrying the side switch wipers 128, 129, 130 and 131 to second position. By this operation the side switch wiper 131 is carried into connection with ground G thereby closing the energizing circuit of the rotary magnet 37. The rotary magnet, upon energizing, rotates the shaft and wipers into engagement with the first trunk, and at the sametime depresses the armature of the private magnet, thereby placing thesidc switch in readiness to pass to third position as soon as the armature of the private magnet is permitted to-return to normal. This will, of course, occur if the first trunk is idle, because as the rotary armature falls back there is nothing to hold the private armature depressed. But if the first trunkis busy the'private wiper 132 will find the private contact 74: grounded, thereby energizing the private magnet 39 and retaining the said private magnet energized as long as the private wiper 132 continues to find guarded contacts. The energizing circuit for the private magnet in this case is from ground, as, for example, from ground G at the relay 71 to the private contact 74, private wiper 132, back release relay :0 (which is low-wound), side switch wiper 130 in second position, and private magnet 39 to battery B. The Side 100 switch being thus retained in second position, the energizing circuit for the rotary magnet 37 is thus prolonged until an idle trunk is found, at which time the private magnet armature, upon falling back, per- 105 mits the side switch to pass to third position,

thereby cutting the subscribers line through :to the trunk H by way of theside switch wipers 128 and 129 third position and the shaft wipers 133 and 2134-. It will be seen, furthermore. that as soon as the side switch passes to third position the side switch wiper 130 supplies ground from ground G to 'the private wiper 132, and

thereby causes the energizationof the relay i to battery B. The energizing circuit of the relay 39 is as follows: from the same ground G to the same conductor 135, thence to the conductor 138, through the springs 83 and 84 of the,,switch l and through the relay 89 to battery B. The relay 70, upon -energizing, energizes the winding 73- of the switch l' by a flow ofcurrent from ground 13o .gagement with the spring G at the relay 70, through 'the springs 139 and 140, conductor 141 and through the winding 73 to battery. The winding-73, upon energizing, attracts the armature 79, which thereupon disconnects the springs 81 and 82 and the springs 83 and 84, and carries the springs 85 and-=86 'into contact. The separation of the springs 81 and 82 disconnectsthe line winding 77 from the rotary conductor 142. thus leaving the trunk clear.

' 'The closure of contacts 85 and 86 is made preparatory fora release when the switch F is disconnected. from the trunk, and the springs 83 and 84 are separated for breaking the energizing circuit of the relay 89. It therefore follows that;the relay 89 is only energized for a moment, with the ,result that the spring 143 is carried into en- 144, while' disconnected from the spring 145. The engagement of the springs 143 and 144 sends an impulse over 4 in the non-numerical switch M by a iiow of current from ground (i over the conductor 146, conductor 147, through the springs 102 and 101 of the switch M, through the line winding 100, relav 115, springs 148 and 149, springs 150 and 151 to battery lead 152, and through the battery B to ground GR When the line winding 1'00 energizes, the

armature 109 is attracted and the springs 108 and 107 are carried into contact, thereby closing an energizing circuit for the trip winding98, since the same'circuit that energizes the winding 100 alsoenergizes he slow-acting relay 115, whereby the sprigs 153, 154 and 155 are pressed The energizing circuit for the trip winding 98- therefore is as follows: from ground. G" at the relay 93 of the A -exchange through the springs 156 and 157-to the conductor 158, through the springs 107 and 108, winding 98, springs 153, 154 and 155, conductor 159, rings 150 and 1.51 to the' battery lead 102, and through battery B to ground G It willbe seen that the relay 115 not only closes the energizing circuit for'the trip winding 98, butit also closes an ener- 'zing circuit for :the auxiliary slow-actmg relay 116. The said relay 116, upon energizing, operates the springs 148 and 149, and thus destroys the cnergizing cir cuit for therel'ays 115'and 100. The relay 89,;like its corresponding relay96,is herein shown slow in order that the length of the impulse that energizes the relays 100 and a lay for the relay 1 6 and for the trip winding 115 may be controlled; but the impulse of these relays may,.of course, be made of any desired length. This is also true of the relays 114, 115 and 116. As. soon as the re- 115 .deener i7es, the energizing circuits 98 is broken but in the meantime the wind ing 98 has had opportunity to attract the the conductor 146 for trip-.

into contact.

-.contact 177 of the switch F armature 111 and thus press the bank springs 160 and 161, the springs 162 and 163, the springs 164 and 165, and also the springs 166 and 167 into contact. Of course. the closure of contact between thesprings 160 and 161 on one side. and 166' and 167 on the other, extends the calling subscribers line over the trunk H to the second.-selc battery 1ead'l52. The non'numerical switch M, unlike the line switch I), must hold its armature down-or it will return to normal. and for this reason it is necessary to energize the bridge-cut-ofi winding 99; but since it requires very little force to hold the plunger down after it is once down, the windii g 99' is made ofhigh rcsistance in fat-thigh enough to prevent the relayllfi from energizing in series therewith. Of course, when thearmature 111 is attracted. then the armature .110 is depressed and the springs 106 and-105 are held in contact, but the springs-104 and 103 are separated. as well i as the springs 102and 101. It will be seen that as soon as the springs 164 and 165 (lo-w in contact a guarding potential is (stain lished from battery 13- through the resistance coil 169to the master switch hank con tact 170 for the purpose ofdriving the mas terswitchfrom opposite the trunk line representing the switch L. The action of the master switch E is the same as theaction of the master switch E. The motor relay closes the energizing circuit for the-motor magnet 113 which then, by operating the first stepcloses its own circuit through springs 171" and 172 to insure the mainte nance of itsown circuit .until the master switch has arrived opposite the next trunk.

From theprevious description'it will be seen that the locking circuit for the bridge cut-off winding 99 of the switch M contains the relay 94.- This relay '94 energizes.v together with the winding99, and, upon energizing, operates the springs 173 and 174 for breaking the circuit of the" relay 93: and

atthe same time the relay 94, by pressing the. springs 175 and.176 into contact, supplies guarding potential at the private bank and to all mul-. tiples thereof in order to make the trunk ll busy to the exchange A,

' The connection between the calling subseriber and theswitch L having been thus completed by the stopping of the switch F (Fig. 1) on the trunk the circuits are now prepared to receive the impulses corresponding to the second digit 2, which the subscriber sends in by operating his dial a second time.I Upon operating the dial for the second digit 2 two impulses are transmitted to the vertical conductor 12, and one impulse to the rotary conductor 13. It should be stated that thepreliminary impulse which is now sent in over the rotary line conductor 13 is received at the selector 1 is in normal-position does not operate to change the condition of these switches. The vertical impulses that are sent in by the subscriber upon the operation of his dial for the second digit operates the vertical line relay 48, which in turn operates the vertical magnet 50 to raise the shaft and wipers to the proper level, in this case the second level. As in the selector F the shaft remains in this position until the rotary impulse is sent in, at which time the rotary line relay 49 is energized, which relay in turn operates the privatemagnet 53, causing the side switch to trip to second position, thereby closing the energizing circuit of the rotary magnet 51, thus bringing about the conditions which a cause the selector L, as the selector F, to antomatically rotate until an idle trunk is found. In this case the trunk found is represented as being the trunk terminating in the connector switch K. Of course, as soon asv the selector switch L stops on the trunk that terminates in the connector switch K, theside switch passes to third position, and

guarding potential is set up as the private wiper 178 from ground G1", while the line relay 55, thereby in turn energizing the vertical magnet 57 from ground G and raising the connector switch shaft two steps to apoint opposite thefirst contact of the second level. The rotary impulse'that is, the impulse to the rotary line conductor 13-which follows then operates the rotary line relay 56, which relay in turn energizes the/private magnet 60 by a flow of current from ground G through the private magnet (30, and through the springs 1 83 and 184 to the battery lead 152, thence to battery 13 and to ground G By this operation of the private magnet 60 the'side switch isallowed to pass to second position, whereby the rotary magnet 58 is put under the control of the vertical line relay in place of the vertical ten vertical impulses to the vertical line conductor 12 energize the vertical line relay 55 ten times, whereby therotary magnet 58 is energized ten times, and the shaft and shaft wipers are so rotated that the wipers engage the terminals 185, 186 and 187 of the switch D of the called line. The rotary impulse that follows energizes the rotary line relay 56, which in turn energizes the private magnet 60 as before, thereby tripping the side switch to third position.

In the third position the side switch wiper 188, by closing the circuit to ground G establishes a guarding potential at the private normal 187 of the called line so as to make the called line busy. At the same time the line circuit is 'ex'tendedfrorn the calling telephone through the side switch wiper 189 and line shaft wiper 190 on one side, and through the side switch wiper 191 and the line shaft wiper 192 on the other side, to the line conductors 193 and 194 of the called line. After the side switch has passed to third position the calling subscriber presses his signaling button 195, thereby ground? ing the vertical line conductor 12 and thus energizing the vertical line relay 55 and the difi'erential'relay 62.- A a result the ringer relay 61 is energized from ground G through the side switch wiper 196, ringer relav 61, and through the differential relay springs 197 and 198 to the battery lead 152, thence through battery B to ground G The ringer relay (31. upon energizing, throws the ringer generator 185' across the called subscribers line, thereby signaling the said subscriber whose bell is across the line as long as his receiver is on the hook. As soon as the called subscriber removes his receiver from the hook he throws his transmitter across the line conductors 193 and 194 in place of the ringer. As a result, a circuit is established through the transmitter 1880f the called telephone, which circuit includes the windings of the backbridge double-wound relay 63. This circuit may be traced from ground G at the connector through the side switch wiper 188, through the winding 187 of the'coil 63 to one side of the called line 194, thence throughthe transmitter to the other sideof the line 193, back through the other winding 188 of the coil 63, through the springs 189 and 198 to the battery lead 152, thence to battery B The relay Q8 therefore energizes, thereby shifting the spring 183 from the non-grounded battery ,spring 184 to the grounded battery spring 190. thus supplying talking battery current to the calling telephone line. The flow of current is as follows: from ground G through the springs 190 and 183, through one winding of relay 62 and the rotary line relay 56 to the calling telephone and back on the other side, through the vertical line relay thus energizing, disconnects the trip magnet 6% from the line and at the same time cuts the vertical normal conductor 185 through to the vertical line conductor 193.

After the subscribers are through talking, if the calling subscriber hangs up his re ceiver first he presses the release springs 15, 16 and 17 together, thereby grounding both sides of the line at the same time, thus energizing the auxiliary back-release relays 67 and 68 (Fig. 1) at the same time, and also the connector line relays and 56 and the differential relay 62. The energizing of the relays 67 and .68 at the same time presses the springs 199 and 200 into contact, thereby closing an energizing cir uit for the back-release relay 4.0 of the selector F, which-in turn, upon energizing closes an energizing circuit for the release magnet 38 by pressing the springs 201 and 209. into contact. The release magnet 38 in turn closes an energizing circuit for the line switch release magnet "21, which latter withdraws the plunger from the bank. In this w ay the selector switch F and the line switch. Dare restored, and a similar energization of the connector line relays 55 and i and of the double-wound coil 62 closes an en gizing circuit for the release mag- ?il? oi? the connector in series with the backa'elease relay 54- ot the secood-selector L. This ener izing circuit may be traced from ground (1 at the second selector L throiiigh the back-release relay 54, springs 203 and 204, release magnet59, springs 197 and 198 to the battery lead 152, and through battery B to ground G. The connector switch is thus released, whereby the line switch I) of the called station is likewise released. The second-selector back-release relay 54, uponenergizing, closes an energizing circuit for the release magnet 52,

whereby the selector L is released, while the release magnet 52, upon energizing, breaks the locking circuit through the winding 99 of the switch M, thus restoring the switch M to normal and at the same time restoring the relay 94 (Fig. 3).

It will be seen that when the selector F (Fig. 1) leaves the trunk H, the energizing circuit for the relay 70 is broken, and therefore the energizing circuit for the bridgecut'oil winding 73 of the trunk switch I is broken, whereby the armature 79 is allowed to return to normal, and in this manner the central oiiice apparatus is completely restored. it will be seen that if the called subscriber had hung up 'before the calling subscriber, the connection would nothave been released until the callingsubscribcr had hungup, the only difference intne. condition being that if the callingsubscriber had hung. up first he would havehad to re lease while there was battery in the talk-- ing circuit, as explained, which battery is out off as soon as the-double-wound coil 62 at the connector energizes, since assoon as this coil energizes the circuit of the backbridge coil 63 is broken. It will be seen that if the called subscriber had been busy when the connector K attempted to pass the side switch to third position by energizing the rotary line relay 56, instead of the connection being established the connector switch wouldhave been released as follows: The side switch being in second position and there being ground at the normal conductor 187, an energizing circuit would have been established through the release magnet 59 at the instant that the private magnet '60 was energized. This energizing circuit may be traced as follows: from ground at the I conductor 187 through the sideswitch wiper 188 in second position, through the top pair of the private magnet springs, through the release magnet 59, and through the springs 197 and 198 of the coil 62 to the battery lead 152. It will be seen, of course, thatat the time the rotaryline relay 1-56 is, being energized the coil 62 is at the same time energized, and that therefore the springs 198 and 197 are in coi'itact. The connector having thus been released, then when the subscriber attempts to signal by pressing his button 195, instead of ringing the called subscriber as he intends, he energizes the vertical line relay 55,,which raises the connector switch shaft and closes the busy-signaling circuit to the calling line by pressing 1 the contacts 205 and 206 togethen. lt will be seen that it the subscriber J had wished to call the subscriber (l the connection would have been made by first operating the line switch D (Fig. 3),thereby establishing connection with some first-selector such as the first-selector F, which in turn would have been operated to select the trunk H, thereby tripping the switch I at the A-exchange, and thus establishing connection with a secondselector such as the second selector L.

through which a connector such as the con nector K would be reached, and through the medium of which final connection with the desired subscriber would be established in the same manner as heretofore described. In an exchange of this character it becomes necessary that the switches such as the sc-. lector F (Fig. 1 should be inspected and tested out, and in the course of these operations the switches F may be operated manually and caused to stop on a trunk H. The effect of this operation. it will at once be seen, is that the trunk switch M at the exchange A is operated, and it therefore be.- comes important that as soon as the switch Fis removed from the trunk manually th'e trunk and its switches will be automatically restored so ,normal. This is-in fact what will occur. {As soon as the switch F is force- 'gfully removed from the trunk the ground is,

. I of course, removed from the private contact '74, with the result that the relay 70 is deenergized. The relay 70, upon permitting its armature tofall back, allowsthe spring 139 to pass,intolengagement witlrthe contact 207 before it leaves the contact 140. As soon 'as connection is established with the l Contact 207 the forward release relay (39 is --'energized over the following circuit: from ground G through the springs 139 and 207, conductor 208, through the trunk -switch 1 's'prings 85 andSG, conductor 209, relay 69, through thesprings 136 and 137 to battery Y B and to ground G. As a result, the conductors 142 and 210 are grounded, thereby energizing the line relays 4S and 49 of the "selector L. These relays 48 and 49. upon energizing, press the springs. 211, 212 and 213 1nto'contact, thereby energizing the pr1 vate magnet 53, winch latter, by pressing the -springs 214 and 215' into contact. closes an energizing circuit through the release mag net 252'by wayof the springs 212 and 21h. The release magnet of course. separates 'the' s IHWS 2-16 and 217. therebv unlockm the trunk switch M and restoring the same, Of course, as soon as the relay T0 falls back sufliciently to separate the springs 139 and 14:0,the energizing circuit of the bridgecut-off winding .73 of the switch I is broken. and the armature 79 permitted to return to normal. v

From the foregoing it will be seen that byimy inventionl provide a two-way trunk for use in connection with a three-wire sys tem. whereby two-way trunking is accomplished without the danger of a trunk being made .busv when one of the seizing switches stops 0 10 trunk, and left busy after the seizhnien u...1- is disconnected from the trunk in some manner otherwise. than electricall v.. Furthermore. with my improved two-way trunk arrangement the switches can be inspected and tested at the exchange by manually causing a switch to receive one of thetwo-way trunk lines, and at the sametimeautomatically making the trunk busy at both ends. And to this, of course, is added the feature already explained, namely that when'the exchange inspector releases the switch-he 1s testing (In a mechanical manner)tha't is, by forcefully and mechanically releasing the san1e'th'ere is then no danger of the other end of the trunk being left in a-busy condition: and consesequently the S\\'lt(l16S can be freely tested without danger of leaving "the two way trunk in a busy condition. as has heretofore becnthc case in certain kinds of apparatus. My invention, it 'Wlll be seen, relates to closed in United States Letters Patent Nos.

815,1 76 and8l5,32l, ranted March 13, 1906, to Keith, Erickson 8: Erickson, British Patent No, 26,301 of 1906, the lles tern, Electrician o? Chicago, Illinois, of January 25,

1908, and in the American, Telephone Journal of New York, N. 'Y., of June 6, 1908. \Vhat lclaim as my intention is I. In a telephonesystem, a two-way trunk line, a non-numerical switch for each end of the trunk line, a switch for seizing the trunk at one end, means whereby thenon-numerical switch at the other end is then automatically and at once operated to make connection with another line, and whereby the nonnumerical switch at the one end of the trunk line is automatically cut oii', and means for sending impulses over one. side only and subsequently over the other side of the trunk for operating purposes.

In a telephone system, a two-way trunk line. a non-numerical switch for each end of the trunk, a switch for seizing the trunk at one end, means whereby the non-numerical switch at the other end; is operated to automatically set up a connection with another line when the trunk is thus seized, and whereby the non-numerical switch at the one endnfthe trunk line is automatically cut off, and the trunk is made busy at both ends as soon as seized, and means for sending im pulses over either one of the trunk conductors separately.

In a telephone system, a two-way trunk line, a non-numerical switch for each end of the trunk line, a switch for seizing the trunk at one end, means whereby the lion-numerical switch at the other end is then automatically and at once operated to make connection with another line. and whereby the non numerical switch at the one end of the trunk line is automatically cut oil, and means for sending impulses over one side only and subsequently over the other side of the trunk for operatingpurposes, together with means whereby, whenever the seizing switch is disconnected from the trunk in any manner, both of the non-numerical switches are automatically restored.

4. In a telephone system, a two-way trunk line, a non-numericalswitch for eachend of the trunk, a switch for seizing the trunk at one end, means whereby thQ'non-nume'rical switch at the'other end is operated to automatically set up a connection with another. line. when the .trunk is 'thus seized, and whereby the non-numerical switch at the one end the trunk line is automatically cut off, and the trunk is made busy at both ends-asls'rion as seized, and means for sending impulses over e1ther.one or the trunk connected from the trunk in any manner,

both of the non-numerical switches are autoi'naticalla' restored. y

fir/In a telephone systen'i, a trunk adapted for making;connection between two exchanges' or points in either direction, a nonnumerical switch at each end of the trunk, a switch forseizing the trunk at one exchange, and a switch for seizing the trunk at the other exchange, means whereby, whenever the trunk is seized at either end, said nonnumerical switches at both ends are disconnected from the trunk, and at the same time the non-numerical switch at the opposite end of the seizing switch is automatically operated to set up a connection with another line, .and nieans for sending impulses over either side of the trunk separately 6. In a telephone system, a two-way trunk line, a non-numerical switch for each end of the trunk line, a switch 'for seizing the trunk atone end, means whereby the non numerical switch at the other end is then automatically and at once operated to ma he connection with another line, and whereby the non-numerical switch at the one end of the trunk line is automatically cut off, and means for sending impulses over one side only and subsequently over the other side of the trunk for operating pur 'ioses, in combination with means whereby two telephone subscribers may be connected together for conversational purposes over a circuit including the said trunk, and whereby battery current'may be supplied to both of the subscribers for talking purposes from a source other than at the telephone.

7 In a telephone system, a two-way trunk line, a non-numerical switch for each end of the trunk, a switch for seizing the trunk at one end, means whereby the non-numerical switch at the other end is operated to autmnatically set up a connection with another line when the trunk is thus seized. and

whereby the non-numerical switch at. the

' for talking purposes from a sour e other than at the telephone.

8. -In a telephone system. a two-way trunk line, non-nun'iericz'd switch for each end of the trlhik-line, a switch for seizing the trunk at one end, means whereby the nonnumerical switch at the other end. is then automatically and at once operated to make connection with another line, and whereby only and subsequently over the other side of .the trunk for operating purposes, together with means whereby, whenever the seizing switch is disconnected, from the trunk in any manner, both -of the non numerical switches are automaticallyrestored,.in combination with means whereby two telephone subscribers may be connected together for com-'ersational purposes over a circuit including the said trunlgand Whereby battery current may be supplied to both of the subscribers for talkingpurposes from a sourceother than at the telephone.

9. In a telephone system, a two-way trunk line, a non-numerical switch for each end of "the trunk, a switch for seizing the trunk at one end, means whereby the non-numerical switch at the other end is operated to automatically set up a connection with another line when the trunkis thus seized, and whereby the non-numerical switch at the one end of the trunkline is automatically cut off, and the trunk is made busy at he ends as soon as seized, and meansfor sending impulses over either one of the trunk cornluctors separately together with means whereby, whenever the seizing switch isdisconnected from the trunk in any manner, both of the non-numerical switchesare automatically restored. in combination with means whereby two telephone subscribers may be connected together for conversational purposes orer a circuit inclilding the said trunk, and whereby battery current may be supplied to both of the subscribers for talking purposes from a source other than at the telephone.

10. In a telephone system. a trunk adapted for connection between two exchanges or points in either direction. a non numcrical switch at each end of the trunk. a switch for seizing the trunk at one exchange. a switch for seizin; the trunk at the other exchange. and means whereby. whenever the trunk is seized at either end. said non-numerical switches at both ends are disconnected from the trunk. and at the same time the ll0ll-llllIl|(.ll(f1ll switch at the opposite end of the seizing switch is automatically operated to set up a connection with another line, in combination with means wherein; two telephone snhscribers may be connected together forconversational purposes over a circuit including; the said trunk, andwherchy battery current may -be supplied toboth of the subscribers for talking purposes from a source other than at the telephone, and means for sending impulses' over either side of the trunk separately.

11. In a telephone system, a two-way trunk line, an automatic non-numerical trunking swit h for each end of said line *ing connection; from; sai

g n jiiidividual thereto; means for conveying mg impulses oventh-talking conductors pulses, and means for talkihgover said conductors.

12.111 a telephone. system, a two-way trunkline, an 4 automatic 'non numerical trunking switch' for-each endofl said line and individual thereto, instrumentalities operative to make either end of the line busy iwhen'the otherend is seized, means for conveying calling impulses over .the -talking .conductors of said trunk separately and at different times, and for simultaneouslyconveying' impulses, and means for talking over a said conductors."

I I v 13.- In a telephone/(system, a two-way trunk line,v a non-numerical; trunking switch for eachend of/said,line, ;each switchextend a trunk adapted 'to' automaticaillg tion "of the called subscriber, numerical trunking switches for seizing either end of said trunk.line,. and instrumentalities operative to'render either end of said trunk line busy ,when the other end is! eiz'e'd, means for conveying impulses over the conductors of said trunk separately fnd at different 30 times, and'for simultaneously conveyingim- 14. In. a telephone system, two-way i '.,-trunkline, a non-numerical trunking switch a (f; for each .end of said, a line and individual thereto,- inst'rumentalities operative to make both ends of said trunk-line busy when either end thereof is seized, means -for conveyin g -'calling impulses. over the talking conductors of said trunk'separatelyand at different times, and for simultaneously conveying impulses, and means for talking over Isaid-conductors. a" telephone system, a two-way trimk line, a non-numerical trunking s' itch for 'each' ehd of said line, each switch adapted-to automatically extend a trunking connection from said line in the direcid -trunlgseparatilyand at difierent 1311119 and fo flsimultaneeusly conveying. im-

Him in the direc-.

tion of ;the called subscriber, numerical trunking switches for seizing either end of said trunk-line, and instrumentalities operative to render both ends of said trunk line busy when either end thereof is seized,

and means for conveying impulses over the trunk conductors separately and at difierent times, and for simultaneously convey-v ing impulses:

16. In aytelephone system, a. set Of'tWD-y way. trunks, a set of non-numerical tru nkin switches for the said trunks at one en thereof, a] master switch for said set of trunking switches, another set of non-numerical switches for said trunks at the other end thereof, and another master switch for said last-mentioned set of trunkingswitches, -means for conveyingimpulses" over the conductors of each-of said trunks separately andat 'diiferent' times, and for simultanetrunkconductors separately and at different .times,-and for'simultaneously conveying impulses.

18. trunk line,an automatic switch at each end I of said line for seizing the same, means for rendering said trunk line busy at both ends when said trunk is seized by a direct hand operation of either of said switches; and

means for automatically removing'said busy condition from the trunk when the seizing switch is disconnected from the trunk.

. Signed by me at Chicago, Cook county,

- Illinois, this 25th day of November, 1908.

EDWARD D. rA Es witnesses:

J. Nomsr, C. E. TAYLOR.

In a telephone system, a twoay 

